The extraction of cholesterol oxidase from cholesterol oxidase producing microorganisms utilizing nonionic surfactants is well known in the art.
The extraction of cholesterol oxidase produced by various microorganisms utilizing aqueous nonionic surfactant solutions is described, inter alia, in U.S. Pat. Nos. 3,907,642 and 3,909,359 as well as British Pat. Nos. 1,385,319 and 1,391,876.
Anionic exchangers, well known and utilized in the art, do not produce a cholesterol oxidase preparation substantially free of the nonionic surfactants utilized in the extraction of cholesterol oxidase from microorganisms.
Ammonium sulfate precipitation of cholesterol oxidase from an aqueous processing solution, well known and utilized in the art, does not result in a cholesterol oxidase preparation substantially free of the nonionic surfactants utilized in the extraction of cholesterol oxidase from microorganisms.
The level of surfactant present in a cholesterol oxidase preparation affects the calibration of a cholesterol assay utilizing cholesterol oxidase bacause a given amount of surfactant is added to the assay mixture in order to solubilize the cholesterol and facilitate the binding of cholesterol to cholesterol oxidase. If excessive surfactant is present in the cholesterol oxidase preparation, the rate of binding of cholesterol to cholesterol oxidase is not reproducible from lot to lot of the cholesterol oxidase preparation, thus making calibration of a cholesterol assay difficult.
In a cholesterol assay utilizing a immobilized cholesterol oxidase preparation, the use of a cholesterol oxidase preparation (substantially free of surfactant) would be advantageous because of decreased surfactant interference with the immobilization of cholesterol oxidase.
A cholesterol oxidase preparation which is substantially free of nonionic surfactant can be further purified, if desired, more easily than a cholesterol oxidase preparation containing excessive surfactant.